Furnace header box having blocked condensation protection, a furnace including the header box and a blocked condensation protection system

ABSTRACT

A header box, a furnace and a blocked condensation protection system are disclosed herein. In one embodiment, the header box includes: (1) a first channel having a first channel supply port positioned to be in fluid communication with an inlet of a combustion air blower and a first pressure port couplable to a first input of a pressure sensing device, the combustion air blower and the pressure sensing device associated with the cold end header box and (2) a second channel having a second channel supply port positioned to be in fluid communication with the inlet of the combustion air blower, a second pressure port couplable to a second input of the pressure sensing device and a pressure reference inlet, the second channel in fluid communication with the first channel and configured to have about a same pressure as the first channel when the pressure reference inlet is blocked.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/295,501, filed by Shailesh S. Manohar, et al., on Jan. 15, 2010,entitled “An Improved Heating Furnace for a HVAC System,” andincorporated herein by reference.

TECHNICAL FIELD

This application is directed, in general, to furnaces and, morespecifically, to protecting the furnace from condensation accumulation.

BACKGROUND

HVAC systems can be used to regulate the environment within anenclosure. Typically, an air blower is used to pull air from theenclosure into the HVAC system through ducts and push the air back intothe enclosure through additional ducts after conditioning the air (e.g.,heating or cooling the air). For example, a furnace, such as a gasfurnace may be used to heat the air.

High efficiency residential gas-fired appliances typically rely on amechanical means, such as a combustion air inducer, to create controlledmass flow thru the flue side of the appliance heat exchanger. For flowto occur, a pressure differential must exist across the heat train ofthe furnace. To verify that the proper pressure drop and flow areachieved and maintained to support the combustion process of the furnacewithin safe limits, pressure sensing devices are typically employed.These pressure sensing devices might include mechanical differentialpressure sensing devices (such as pressure switches) or electronicsensors which provide feedback to an integrated electronic control.

This type of furnace design is similar among industry manufacturers, andtypically employs a flue gas/condensate collector box attached to theend of the condenser coil (referred to herein as a Cold End Header Box(CEHB)), a combustion air inducer fan assembly (CAI), a fixed orificelocated in the CAI or CEHB to regulate flow through the heat train, anda pressure sensing device to monitor flow. The pressure sensing devicecould be used to monitor pressure across the fixed orifice, or otherpoints in the heat train to provide the most advantageous signal for theapplication.

SUMMARY

In one aspect, the disclosure provides a CEHB. In one embodiment, theCEHB includes: (1) a first channel having a first channel supply portpositioned to be in fluid communication with an inlet of a combustionair blower and a first pressure port couplable to a first input of apressure sensing device, the combustion air blower and the pressuresensing device associated with the cold end header box and (2) a secondchannel having a second channel supply port positioned to be in fluidcommunication with the inlet of the combustion air blower, a secondpressure port couplable to a second input of the pressure sensing deviceand a pressure reference inlet, the second channel in fluidcommunication with the first channel and configured to have about a samepressure as the first channel when the pressure reference inlet isblocked.

In another aspect, a furnace is disclosed. In one embodiment, thefurnace includes: (1) a heat exchanger, (2) a combustion air inducerconfigured to generate air flow through the heat exchanger, (3) apressure sensing device configured to monitor a combustion pressurethrough the heat exchanger and (4) a header box configured to be coupledbetween the heat exchanger and the combustion air inducer, the headerbox having: (4A) a negative pressure channel having a first channelsupply port positioned to be in fluid communication with an inlet of thecombustion air blower and a negative pressure port couplable to anegative input of the pressure sensing device; and (4B) a positivepressure channel having a positive pressure channel supply portpositioned to be in fluid communication with the inlet of the combustionair blower, a positive pressure port couplable to a positive input ofthe pressure sensing device and a pressure reference inlet, the positivepressure channel in fluid communication with the negative pressurechannel and configured to have about a same pressure as the negativepressure channel when the pressure reference inlet is blocked.

In yet another aspect, blocked condensation protection system for afurnace is disclosed. In one embodiment, the blocked condensationprotection system includes: (1) a pressure sensing device configured tomonitor a combustion pressure through a heat exchanger of the furnaceand (2) a header box configured to be coupled between the heat exchangerand a combustion air inducer of the furnace, the header box having: (2A)a first channel having a first channel supply port positioned to be influid communication with an inlet of a combustion air blower associatedwith the furnace and a first pressure port couplable to a first input ofthe pressure sensing device and (2B) a second channel having a secondchannel supply port positioned to be in fluid communication with theinlet of the combustion air blower, a second pressure port couplable toa second input of the pressure sensing device and a pressure referenceinlet, the second channel in fluid communication with the first channeland configured to have about a same pressure as the first channel whenthe pressure reference inlet is blocked, the pressure sensing deviceconfigured to turn off a fuel supply to the heat exchanger whendetermining a pressure differential between the first channel and thesecond channel is about zero.

BRIEF DESCRIPTION

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is an exploded isometric view of a portion of an embodiment of afurnace constructed according to the principles of the disclosure;

FIG. 2 is a front isometric view of an embodiment of a CEHB constructedaccording to the principles of the disclosure;

FIG. 3 is a rear isometric view of the CEHB of FIG. 2;

FIG. 4 is a functional view of an embodiment of a CEHB constructedaccording to the principles of the disclosure showing normal operationwhen the CEHB is in a horizontal position;

FIG. 5 is a functional view of the CEHB in FIG. 4 illustrating a blockeddrainage path;

FIG. 6 is a functional view of an embodiment of a CEHB constructedaccording to the principles of the disclosure showing normal operationwhen the CEHB is in an upright position;

FIG. 7 is a functional view of the CEHB of FIG. 6 illustrating a blockeddrainage path; and

FIG. 8 is a block diagram of an embodiment of a blocked condensationprotection system constructed according to the principles of thedisclosure.

DETAILED DESCRIPTION

As air flows through the heat train of the furnace, condensation isgenerated and typically collected in the CEHB. To prevent build-up ofthe condensation and protect the monitoring equipment, for example thepressure sensing devices, proper draining of the condensation out of theCEHB is needed. Conventional furnaces may require multiple pressuresensing devices or require relocating the pressure sensing devices whena furnace is used in different positions in order to properly sensewater build-up under block drain conditions and protect the sensingdevices from condensation. Additionally, hoses used for drainage orsensing pressure may also have to be relocated when a furnace isinstalled at different positions.

The disclosure provides a furnace including a header box havingintegrated blocked condensation protection. Whether the furnace isinstalled in either an upright or horizontal position, disclosed hereinis a blocked condensation protection system that is configured to shutoff the fuel to the furnace when the condensate drain, a vent or an airintake is plugged. Instead of the disclosed furnace requiring multipleswitches for monitoring combustion pressure (which verifies proper flowthrough the heat exchanger), as disclosed herein a single pressuresensing device may be used to monitor the combustion pressure andprotect against blocked condensation drainage. Unlike conventionalfurnaces, the disclosed furnace does not need the relocating of switchesor the rerouting of any pressure tubes when used in different positions.

In one embodiment, the header box is a CEHB of a gas furnace. The CEHBis disposed between the secondary heat exchanger and the combustion airinducer of the gas furnace. The disclosed CEHB includes channels thatare appropriately sized and positioned to fluidly communicate and obtainabout the same pressure when condensation drainage is not operatingproperly (e.g., blocked condensation). As such, a pressure sensingdevice coupled to pressure ports in the channels detects a zero or aboutzero differential pressure between the channels and shuts off the fuelsupply to the furnace. Due to the configuration of the channels, thedisclosure advantageously uses a single pressure sensing device tomonitor the combustion pressure and blocked drainage. Advantageously,the number of safety pressure switches that are typically needed can bereduced.

Turning now to FIG. 1, illustrated is an exploded isometric view of aportion of an embodiment of a furnace 100 constructed according to theprinciples of the disclosure. The furnace 100 may be a multi-positionfurnace. In some embodiments, the furnace may be a residential gasfurnace. The furnace 100 includes an embodiment of a header box havingblocked condensation protection integrated therein. The furnace 100includes a housing 110 having a front opening 112 within which amounting shelf 114 is located. The mounting shelf 114 has an opening 116therein and supports a heat exchanger assembly 120 over the opening 116.The heat exchanger assembly 120 includes a primary heat exchanger 122and a secondary heat exchanger 126. The primary heat exchanger 122includes a row of six heat exchangers (one referenced as 124) coupled toone another. The heat exchangers are generally serpentine and have threeapproximately 180° folds such that the heat exchangers cross over theopening 116 four times, terminating in inlets 125 (of the primary heatexchanger 122) and outlets 127 (of the secondary heat exchanger 126)that are generally mutually coplanar and oriented toward the opening 112of the housing 110. Alternative embodiments of the heat exchangerassembly 120 may have more or fewer heat exchangers coupled to oneanother in one or more rows. Additionally, alternative embodiments mayhave alternative heat exchanger configurations.

A burner assembly 140 contains a thermostatically-controlled solenoidvalve 142, a manifold 144 leading from the valve 142 and across theburner assembly 140, one or more gas orifices (not shown) coupled to themanifold 144 and one or more burners (not shown) corresponding to andlocated proximate the gas orifices. The illustrated embodiment of theburner assembly 140 has a row of six burners. Alternative embodiments ofthe burner assembly 140 may have more or fewer burners arranged in oneor more rows. A combustion air inlet 146 allows air in for the burnerassembly 140. In an assembled configuration, the burner assembly 140 islocated proximate the heat exchanger assembly 120 such that the burnersthereof at least approximately align with the inlets 125.

The furnace 100 also includes a draft inducer assembly 150 having acombustion air inducer 154 and a combustion flue collar 156 coupled toan outlet of the combustion air inducer 154. In an assembledconfiguration, the draft inducer assembly 150 is located proximate theheat exchanger assembly 120 such that the combustion flue collar 156approximately aligns with a flue (not illustrated) that directsundesired gases (e.g., gaseous products of combustion) away from thefurnace 100. Associated with the draft inducer assembly 150 are firstand second drain hoses, 151, 152, that provide a path to draincondensation from the combustion flue collar 156 and the flue.

A blower 160 is suspended from the shelf 114 such that an outlet (notreferenced) thereof approximately aligns with the opening 116. Anelectronic controller 170 is located proximate the blower 160 and isconfigured to control the blower, the valve 142 and the combustion airinducer 154 to cause the furnace to provide heat. A cover 180 may beplaced over the front opening 112 of the housing 110.

A CEHB 190 provides an interface between the combustion air inducer 154and the secondary heat exchanger 126. The combustion air inducer 154 hasan inlet coupled to the CEHB 190. In an assembled configuration, thedraft inducer assembly 150 is located proximate the heat exchangerassembly 120 such that the CEHB 190 approximately aligns with theoutlets 127 and the combustion flue collar 156 approximately aligns withthe flue.

The furnace 100 also includes a pressure sensing device 195 that isconfigured to monitor the combustion pressure through the heat train ofthe furnace 100. The pressure sensing device 195 may be a mechanicaldifferential pressure sensing device (such as a pressure switch) or anelectronic sensor which provide feedback to an integrated electroniccontroller of the furnace 100, such as the electronic controller 170.The pressure sensing device 195 includes inputs for determining thecombustion pressure. The inputs of the pressure sensing device 195 arecoupled to pressure ports of the CEHB 190. As discussed below, thepressure ports are protected from water contamination by placement ofthe pressure ports in channels of the CEHB 190.

Based on a differential pressure obtained by the pressure sensing device195 from data received via the pressure ports, the gas supply for theheat exchanger 120 may be turned-off or remain off when there isimproper air flow through the heat train. Additionally, the gas supplyfor the heat exchanger 120 may be turned-off or remain off whencondensation drainage of the CEHB 190 is impaired or blocked. Thus, thesame pressure sensing device 195 employing data from the pressure portsof the CEHB 195 may protect the furnace 100 from improper air flowthrough the heat train and protect the furnace 100 from blockedcondensation drainage. The pressure sensing device 195 may be fastenedto the ports of the CEHB 190 through conventional hoses. The pressuresensing device 195 may also be coupled to the electronic controller 170or the valve 142 through conventional means. In some embodiments, thepressure sensing device 195 may be fastened to the CEHB 190.

In the illustrated embodiment, the controller 170 turns on thecombustion air inducer 154 to initiate a draft in the heat exchangers(including the heat exchanger 124) and purge potentially harmfulunburned or combustion gases. Then the controller 170 opens the valve142 to admit gas to the manifold 144 and the one or more gas orifices,whereupon the gas begins to mix with air to form primary combustion air.Then the controller 170 activates an igniter (not shown in FIG. 1) toattempt to ignite the primary combustion air. If the output of a flamerectification circuit indicates that the primary combustion air has notignited within a predetermined period of time, the controller 170 thencloses the valve 142 and waits until attempting to start again. If theoutput of a flame rectification circuit indicates that the primarycombustion air has ignited within the predetermined period of time, thecontroller 170 then activates the blower 160, which forces air upwardthrough the opening 116 and the heat exchanger assembly 120. As itpasses over the surfaces of the heat exchangers, the air is warmed,whereupon it may be delivered or distributed as needed to provideheating.

FIG. 2 is a front isometric view of an embodiment of a CEHB, such as theCEHB 190, constructed according to the principles of the disclosure. Asnoted above, the CEHB 190 is configured to provide an interface betweenthe secondary heat exchanger 126 and the combustion air inducer 154 thatdraws combustion air through the heat exchanger 120.

The CEHB 190 is configured to provide an exit for the heated gas fromthe heat exchanger via the secondary heat exchanger 126. The CEHB 190 isalso configured to remove the condensation associated with the heatedgas. As such, the CEHB 190 is typically constructed of a non-metallicmaterial that is resistive to water corrosion. The CEHB 190, forexample, may be constructed of a plastic.

The CEHB 190 may be employed in a multi-position gas furnace such as thefurnace 100. Accordingly, the CEHB 190 includes components of amulti-position drain system that includes a first drain port 210, asecond drain port 212, a left drain 214 and a right drain 216. The firstand second drain ports 210, 212, are positioned and configured to coupleto drain hoses, such as drain hoses 151, 152, from the combustion fluecollar 156. Depending on the installation of the furnace 100, the leftdrain 214, the right drain 216 or both the left and right drains 214,216, may be used to remove condensation from the CEHB 190.

Located on the four sides of the CEHB 190 is a flange 220 that isconfigured to attach the CEHB 190 to the secondary heat exchanger 126.The flange 220 includes holes, in which hole 222 is denoted, that areused to mechanically attach the CEHB 190 to the secondary heat exchanger126. A gasket is typically used between the flange 220 and the secondaryheat exchanger 126.

The CEHB 190 also includes a support collar 230 that is used to couplethe combustion air inducer 154 to the CEHB 190. The support collar 230,therefore, corresponds to an inlet of the combustion air blower 154 fordrawing air through the heat exchanger 120. The support collar 230 helpssupport the combustion air inducer in such a way that the inducerrequires only two screws compared to the traditional four to mount tothe CEHB 190. A gasket denoted in FIG. 1 is typically used with thesupport collar 230 for coupling the CEHB 190 to the combustion airblower 154.

Located within the circumference of the support collar 230 (andtherefore within the inlet of the combustion air blower 154) is a fixedorifice 240. The fixed orifice 240 is configured to regulate gas flowthrough the heat exchanger 120. The fixed orifice 240 may be sized basedon an input size of the furnace 100. Also located within thecircumference of the support collar 230 are a negative channel supplyport 244 and a positive channel supply port 246. Each of these ports inthe front face of the CEHB 190 provides an opening for supplying air tothe respective channels. The size and location of the fixed orifice 240,the negative channel supply port 244, the positive channel supply port246 and the size and location of positive and negative pressure channels270, 280, (illustrated in FIG. 3) may be determined through empiricaltesting to provide a target pressure or pressure range as detected by apressure sensing device for determining combustion pressure. Theadvantage of such an arrangement is that a common pressure switch, suchas the pressure sensing device 195, can be used for various input sizesof furnaces as well as provide a pressure signal that is suitable to agas-air amplified gas valve to allow input rate modulation.

The CEHB 190 also includes a connection system 235 having alignmentprotrusions as denoted in FIG. 2 that are used to couple the pressuresensing device 195 to the CEHB 190. The connection system 235 and thecorresponding protrusions may vary depending on the type or model of thepressure sensing device 195 to be attached to the CEHB 190.

The CEHB 190 further includes a positive pressure port 250 and anegative pressure port 260 that are coupled to a positive input and anegative input of a pressure sensing device, such as the pressuresensing device 195. The pressure sensing device is configured to monitora combustion pressure across the fixed orifice 240 based on datareceived at the negative input port and the positive input port via thenegative and positive pressure ports 250, 260. The positive and negativepressure ports 250, 260, are typically coupled to the pressure sensingdevice via pressure sensing device hoses. The positive pressure port 250is located within the positive pressure channel 270 and the negativepressure port 260 is located within the negative pressure channel 280 asillustrated in FIG. 3. Locating the positive pressure port 250 and thenegative pressure port 260 within the respective channels and away fromopenings of the respective channels protects the pressure ports and thepressure sensing device from condensation.

The CEHB 190 further includes a screw mounting lug 292 and a water dam295. The screw mounting lug 292 is used when mounting a combustion airinducer to the CEHB 190. The water dam 295 is a condensate water damthat is configured to direct water away from sensitive areas of the CEHB190 and assists in maintaining a stable pressure signal.

FIG. 3 is a rear isometric view of the CEHB 190 that illustrates thepositive pressure channel 270 and the negative pressure channel 280.Though not visible in FIG. 3, the positive pressure channel 270 includesthe positive pressure port 250. During normal operation, the positivepressure channel 270 has the same or about the same pressure as the CEHB190 (i.e., within the main cavity of the CEHB 190). As such, locatingthe positive pressure port 250 within the positive pressure channel 270allows measuring of the combustion pressure while protecting thepositive pressure port 250 from condensation. Other components of thepositive pressure channel 270 and the negative pressure channel 280 thatare not visible in FIG. 3 (or FIG. 2) include the negative channelsupply port 244, the positive channel supply port 246 and a flowrestriction orifice located within the positive pressure channel 270.Additionally, the negative pressure channel 280 includes bleed portsthat are not visible in FIG. 2 or FIG. 3. The bleed ports are configuredto reduce the pressure received through the negative channel supply port244 to a targeted range when measured at the negative pressure port 260.The bleed ports are denoted in FIG. 4. A size, configuration andlocation of the channels 270, 280, and the various components thereofmay be determined through empirical testing to provide a target pressureor pressure range when detected by a pressure sensing device tocorrelate to a targeted pressure drop or flow thru the heat exchanger.

A first end of the positive pressure channel 270, an inlet end 272,extends within the support collar 230 as illustrated within FIG. 4. Asecond end of the positive pressure channel 270, a pressure referenceinlet 274, opens toward the side of the CEHB 190 having the first andsecond drains 214, 216. The pressure reference inlet 274 is located suchthat the collection of an undesired level of condensate within the CEHB190 will cause the pressure within the positive pressure channel 270 tochange. The monitoring of this change by the pressure sensing device 195will allow the furnace to be shut down safely in response to the change.The positive pressure channel 270 has a quadrilateral cross section andincludes four sections that are joined at or about 90 degrees to form acontinuous open channel from the inlet end 272 to the pressure referenceinlet 274.

Though not visible in FIG. 3, the negative pressure channel 280 includesthe negative pressure port 260. The negative pressure channel 280 isconfigured to reduce the high negative pressure that is present at theinlet of the combustion air inducer 154 to a targeted pressure orpressure range at the negative pressure port 260. As such, locating thenegative pressure port 260 within the negative pressure channel 280allows measuring of the combustion pressure signal while protecting thenegative pressure port 260 from condensation. The negative pressurechannel 280 includes a first end denoted as a closed end 282. A secondend of the negative pressure channel 280, an open end 284, opens towardthe side of the CEHB 190 having the first and second drains 214, 216.The open end 284 is located such that the collection of an undesiredlevel of condensate within the CEHB 190 will cause the pressure withinthe negative pressure channel 280 to change. The monitoring of thischange by the pressure sensing device 195 will allow the furnace to beshut down safely in response to the change. The negative pressurechannel 280 has a quadrilateral cross section and includes four sectionsthat are joined to form a continuous open channel from the closed end282 to the open end 284.

Located within a supply section 286 of the negative pressure channel 280is the negative channel supply port 244. A portion of the supply section286 including the negative channel supply port 244 is located within thecircumference of the support collar 230 and, therefore, thecorresponding inlet of the combustion air inducer 154. Sides of thenegative pressure channel 280 around the open end 284 are shaped toprovide a water shroud to protect the negative pressure port 260 fromcontamination.

The negative channel supply port 244 is positioned to be in fluidcommunication with the inlet of the combustion air inducer. The negativepressure port 260 in the negative pressure channel 280 is couplable toan input, such as a negative input, of a pressure sensor device.Similarly, the positive pressure channel supply port 246 is positionedto be in fluid communication with the inlet of the combustion air blowerand the positive pressure port 250 is couplable to an input, such as apositive input, of the pressure sensor device. The positive pressurechannel 270 and the negative pressure channel 280 are in fluidcommunication and are configured to have about a same pressure when thepressure reference inlet 274 is blocked (e.g., blocked by condensation).The CEHB 190 is designed wherein this is true even when the furnaceincluding the CEHB 190 is installed in multiple positions. Duringoperation of the combustion air blower when the pressure reference inlet274 is not blocked (i.e., during normal operation when there is properdrainage), the positive pressure channel 270 is configured to have apositive pressure compared to negative pressure channel 280.

FIG. 4 is a functional view of an embodiment of a CEHB, the CEHB 190,constructed according to the principles of the disclosure showing normaloperation when the CEHB 190 is in a horizontal position (i.e., a furnaceincluding the CEHB 190 is installed in the upflow position. FIG. 4provides a cutaway of the CEHB 190 to more clearly illustrate theoperation of the positive and negative channels 270, 280, within theinlet of the combustion air inducer 154. Illustrated in FIG. 4 inaddition to the previously noted components of the CEHB 190 are bleedports 440 of the negative pressure channel 280 and a flow restrictionorifice 450 of the positive pressure channel 270.

The bleed ports 440 are designed to bleed down the negative pressurethat is received via the negative pressure channel supply port 244. Thebleed ports 440 are positioned in the CEHB 190 to be free from watercontamination. The location and size of the bleed ports are selected tonormalize the high negative pressure in the inlet zone of the combustionair inducer 154 to a targeted pressure value or range of values at thenegative pressure port 260. As such, a single type of pressure sensingdevice can be used for various models.

The flow restriction orifice 450 is configured to restrict air flowthrough the positive pressure channel 270 from the positive pressurechannel supply port 246. The size of the flow restriction orifice 450may be selected to coordinate with the positive pressure port 250.

During normal operation, condensation gathers on the lower side of theCEHB 190, which is connected to both the left drain 214 and the rightdrain 216 when the CEHB 190 is horizontal. Both the left drain 214 andthe right drain 216 can provide a drainage path for the condensation. Insome embodiments, only one of the drains 214, 216, may be used while theunused drain is intentionally plugged.

While a clear drainage path is provided for the condensation to drainout, the pressure reference inlet 274 is unblocked by condensation andthe pressure in the positive pressure channel 270 represents thepressure in the CHEB 190. As such, a pressure differential that existsbetween the negative pressure channel 280 and the positive pressurechannel 270 is maintained.

When the condensation does not drain from the CEHB 190, the condensationbacks-up and blocks the pressure reference inlet 274 as illustrated inFIG. 5. Pressure in the positive pressure channel 270, therefore,becomes more negative based on the input from the positive pressuresupply port 430. As such, the differential pressure between the positivepressure channel 270 and the negative pressure channel 280 is driven tozero or about zero. In response, a pressure sensing device, such as thepressure sensing device 195, that is coupled to the negative andpositive supply ports 260, 250, can initiate turning off the gas to theburners of the heat exchanger 120.

A similar operation is illustrated in FIG. 6 and FIG. 7 wherein the CEHB190 is in an upright position (i.e., the furnace with the CEHB 190 is ina horizontal left or a horizontal right position). As noted in FIG. 6and FIG. 7, the lower side is now the side proximate the pressurereference inlet 274 that is coupled to a single drain (i.e., the rightdrain 216.) FIG. 6 represents proper drainage while FIG. 7 illustratesblocked condensation drainage.

FIG. 8 is a block diagram of an embodiment of a blocked condensationprotection system 800 constructed according to the principles of thedisclosure. The blocked condensation protection system 800 includes apressure sensing device 810 and a header box 820. The blockedcondensation protection system 800 is configured to be used in a furnacesuch as the furnace 100 of FIG. 1. The pressure sensing device 810 isconfigured to monitor a combustion pressure through a heat exchanger ofa furnace. The pressure sensing device 810 may be a mechanicaldifferential pressure sensing device, such as pressure switch.Alternatively, the pressure sensing device 810 may include electronicsensors which provide feedback to an integrated electronic controller.

The header box 820 is configured to be coupled between the heatexchanger and a combustion air inducer of the furnace associated withthe pressure sensing device 810. Some components of the header box 820discussed below are not visible in FIG. 8. The header box is constructedto have at least a portion of blocked condensation protection integratedtherein employing channels that fluidly communicate. The header box 820includes a first channel having a first channel supply port 822positioned to be in fluid communication with an inlet of a combustionair blower associated with the furnace and a first pressure port 824couplable to a first input 812 of the pressure sensing device 810. Theheader box 820 also includes a second channel having a second channelsupply port 826 positioned to be in fluid communication with the inletof the combustion air blower, a second pressure port 828 couplable to asecond input 814 of the pressure sensing device 810 and a pressurereference inlet. The second channel is constructed to be in fluidcommunication with the first channel and configured to have about a samepressure as the first channel when the pressure reference inlet isblocked. The pressure sensing device 810 is configured to turn off afuel supply to the heat exchanger when determining a pressuredifferential between the first channel and the second channel is aboutzero. Having the pressure differential at or about zero indicatesblocked drainage for the header box 820. The header box 820 may be theCEHB 190 as illustrated and discussed above.

Those skilled in the art to which this application relates willappreciate that other and further additions, deletions, substitutionsand modifications may be made to the described embodiments.

What is claimed is:
 1. A cold end header box of a furnace, comprising: afirst channel having a closed end, an open end, a first channel supplyport positioned to be in fluid communication with an inlet of acombustion air blower, and a first pressure port couplable to a firstinput of a pressure sensing device, said combustion air blower and saidpressure sensing device couplable to said cold end header box; a secondchannel having a closed end, an open end, a second channel supply portpositioned to be in fluid communication with said inlet of saidcombustion air blower, a second pressure port couplable to a secondinput of said pressure sensing device, and a pressure reference inlet,said second channel in fluid communication with said first channel; afixed orifice located entirely outside of said first channel and saidsecond channel; wherein said first channel supply port and said secondchannel supply port are different ports and are both located entirelywithin an area of said inlet of said combustion air blower; and whereinsaid first supply port is adjacent said closed end of said first channeland said second pressure port is adjacent said closed end of said secondchannel.
 2. The cold end header box as recited in claim 1 furthercomprising a support collar for coupling said cold end header box tosaid combustion air blower, wherein said support collar corresponds tosaid inlet of said combustion air inducer.
 3. The cold end header box asrecited in claim 1, wherein said second channel is configured to have apositive pressure at said second pressure port compared to a pressure ofsaid first channel at said first pressure port during operation of saidcombustion air blower when said pressure reference inlet is not blocked.4. The cold end header box as recited in claim 1, wherein said secondchannel and said first channel are configured to have about a samepressure at said second pressure port and at said first pressure portwhen said pressure reference inlet is blocked when said furnace is inmultiple installation positions.
 5. The cold end header box as recitedin claim 1 further comprising a first drain in fluid communication withsaid pressure reference inlet and configured to drain condensation awayfrom said cold end header box.
 6. The cold end header box as recited inclaim 5 further comprising a second drain in fluid communication withsaid pressure reference inlet and configured to drain condensation awayfrom said cold end header box, wherein said second drain is located atan opposing side of said first drain.
 7. The cold end header box asrecited in claim 1 further comprising two drains configured to draincondensation away from said cold end header box when said furnace isinstalled in a horizontal position, wherein one of said two drains isused to drain condensation away from said cold end header box when saidfurnace is installed in an upright position.
 8. The cold end header boxas recited in claim 1, wherein said pressure reference inlet is an openend of said second channel that faces a side of said cold end header boxhaving two drains.